Ukraine has announced it has detained two suspected Islamic State militants who Kyiv says were planning to travel to Western Europe to stage terror attacks.

In a statement on June 1, the SBU, Ukraine’s national security service, said the two, allegedly from Syria, were detained in the northeastern city of Kharkiv, although it was unclear when.

"The Kharkiv national security service of Ukraine has uncovered an attempt to send supporters of the Islamic State international terrorist organization from Syria by transit through Ukraine to western European states," the SBU said in the statement.

The SBU said the two were assisted by an individual from an unnamed "neighboring country" who was in the country illegally and wanted by Kyiv on suspicions of possible terrorist activity.

A senior source told the AFP that the individual was a Russian national.

The SBU said it could not provide further details because an investigation was still ongoing.